Image contrast in the backscattered electron mode in scanning electron microscopy and microtomography

The problem of image contrast production in the backscattered electron (BSE) mode in a scanning electron microscope (SEM) in bulk and film structures is discussed. The considerable influence of the parameters of a semiconductor detector on the image contrast is shown. Calculations for contrast in dependence on the composition of target sections, the energy of primary electrons, and the signal detection technique are presented.     

Increasing spatial resolution in the backscattered electron mode of scanning electron microscopy

A new method for increasing spatial resolution in the detection of backscattered electrons and induced current in scanning electron microscopy (SEM) is proposed in terms of regularized Fourier transform. The real size of an electron probe and its blurring in a solid target sample are considered in forming the algorithm. The experiments reveal an almost 100% improvement in resolution in the processed images.     

Site-specific recoil diffraction of backscattered electrons in crystals

A novel diffraction effect in high-energy electron backscattering is demonstrated: the formation of element-specific diffraction patterns via nuclear recoil. For sapphire (Al(2)O(3)), the difference in recoil energy allows us to determine if an electron scattered from aluminum or from oxygen. The angular electron distribution obtained in such measurements is a strong function of the recoiling lattice site. These element-specific recoil diffraction features are explained using the dynamical theory of electron diffraction. Our observations open up new possibilities for local, element-resolved crystallographic analysis using quasielastically backscattered electrons in scanning electron microscopy.     

Shot-noise detection of ultrasound-tagged photons in ultrasound-modulated optical imaging

We propose a new detection method for ultrasound-modulated optical tomography that allows us to perform parallel speckle detection with optimum shot-noise sensitivity, using a CCD camera. Moreover, we show that making use of a spatial filter system allows us to fully filter out speckle decorrelation noise. This method is confirmed by a test experiment.     

Determination of the orientation parameters of grains from the contrast of an image of a multisilicon polished surface using backscattered electrons

The grain structure of multisilicon crystals are investigated by scanning electron microscopy and electron backscatter diffraction. It is found that the contrast of an image obtained by scanning polished multisilicon surfaces in the mode of backscattered electrons by electron-probe microanalysis is caused by the fact that the contrasting grains on the test site of the surface belong to different crystallographic orientations. It is revealed that high-angle grain boundaries are areas where the contrast varies, whereas small-angle boundaries are not observed on the polished surfaces. Consequently, the degree of contrast of the image obtained in this scan mode can be used to qualitatively assess the degree of misorientation of neighboring grains.     

Backscattering target detection in a turbid medium by use of circularly and linearly polarized light

The polarization properties of the backscattered light from a turbid medium containing large-diameter (10.143-microm) and small-diameter (0.202-microm) spherical polystyrene particles are studied. It is shown that the difference in the polarization properties of the emerging light that originates at the target and that is backscattered from the medium allows for improvement of image contrast by use of polarized light. Based on the images obtained by the CCD camera, the polarization memory effect with circularly polarized light is demonstrated to have an advantage over the linear polarization technique in imaging a highly reflective target inside a turbid medium containing large particles.     

Design of a multistage depressed collector system for 1-MW CWgyrotrons. I. Trajectory control of primary and secondary electrons in atwo-stage depressed collector

Part I of this paper presents the design of a two-stage depressed collector for a 110 GHz, 1 MW gyrotron, taking into account the trajectories of electrons backscattered from the electrode surfaces. The collector geometry and the magnetic circuit were adjusted in order to minimize the effect of backscattered electrons. A computer code was employed which is based on a new algorithm designed to give good representation to a variety of energy levels and angles of emergence of backscattered electrons. The collector efficiency estimated on the basis of primary electrons alone was 68%. The estimated collector efficiency which included also the effect of backscattered electrons was 60%. In the latter case the surface of the collectors was assumed to be that of polished copper. The techniques and codes used in the design are reviewed and results of trajectory tracing are presented for primaries and secondaries. Part II of the paper presents the system aspects, including the mechanical and thermal designs and the solid-state power supply design     

Backscattered electron imaging of micro- and nanostructures: 1. Method of analysis

A method for analysis of the formation of backscattered electron scanning electron microscope (SEM) images is described. The results of studying the formation of SEM signals obtained upon scanning an angular structure are given. The mechanisms of the formation of images in the modes of backscattered and slow secondary electrons are described.     

连续照明时成像对比度与气象条件的关系

 通过同轴激光连续照明成像模型分析了大气后向散射对成像对比度的影响，得出了考虑散射因素时成像对比度的计算公式。基于不同气象条件下大气粒子散射特点，讨论了霾和雾两种不同天气时成像对比度随照明距离的变化规律，并与实验结果进行了对比，计算结果与实验吻合较好。     

In vivo dark-field reflection-mode photoacoustic microscopy

Reflection-mode photoacoustic microscopy with dark-field laser pulse illumination and high-numerical-aperture ultrasonic detection is designed and implemented in noninvasively imaged blood vessels in the skin in vivo. Dark-field optical illumination minimizes the interference caused by strong photoacoustic signals from superficial structures. A high-numerical-aperture acoustic lens provides high lateral resolution, 45-120 microm in this system. A broadband ultrasonic detection system provides high axial resolution, estimated to be approximately 15 microm. The optical illumination and ultrasonic detection are in a coaxial confocal configuration for optimal image quality. The system is capable of imaging optical-absorption contrast as deep as 3 mm in biological tissue.     

Thomson-backscattered x rays from laser-accelerated electrons

We present the first observation of Thomson-backscattered light from laser-accelerated electrons. In a compact, all-optical setup, the "photon collider," a high-intensity laser pulse is focused into a pulsed He gas jet and accelerates electrons to relativistic energies. A counterpropagating laser probe pulse is scattered from these high-energy electrons, and the backscattered x-ray photons are spectrally analyzed. This experiment demonstrates a novel source of directed ultrashort x-ray pulses and additionally allows for time-resolved spectroscopy of the laser acceleration of electrons.     

Characterization of semiconductor detectors of (1–30)-keV monoenergetic and backscattered electrons

Semiconductor detectors of backscattered electrons are basic elements of all modern scanning electron microscopes. Their quality is determined by the properties of planar p-n junctions and the parameters of the protective layer on the detector surface. The main characteristics of semiconductor detectors are considered, their response functions are calculated, and the threshold signal cutoff energies are found both for a monoenergetic electron beam and for detection of the total energy spectrum of backscattered electrons. The experimental results are in good agreement with the computational model data.     

Reconstructing the energy spectra of backscattered electrons with allowance for the spectrometer’s response function

The inverse problem of reconstructing the true spectrum of electrons backscattered from massive and layered targets with allowance for the spread function of the toroidal sector energy analyzer and for the response function of the spectrometer??s electron detector is solved. We present the results from studying the energy spectra of a number of homogeneous samples and film-on-substrate systems obtained at different energies of the irradiating electron beam at normal incidence of the electrons on the surface, and at a 45° angle of backscattered electron detection.     

Effect of measurement backaction on adiabatic coherent electron transport

We study the backaction of a nearby measurement device on electrons undergoing coherent transfer via adiabatic passage (CTAP) in a triple-well system. The measurement is provided by a quantum point contact capacitively coupled to the middle well. We account for this continuous measurement by treating the whole {triple-well+detector} as a closed quantum system. This leads to a set of coupled differential equations for the density matrix of the enlarged system which we solve numerically. This approach allows us to study a single realization of the measurement process while keeping track of the detector output, which is especially relevant for experiments. In particular, we find the emergence of a new peak in the distribution of electrons inside the detector, accompanied by a drop in the fidelity of the protocol.     

Visual Passive Ranging Method Based on Re-entrant Coaxial Optical Path and Experimental Verification

To overcome the shortcomings of the traditional passive ranging technology based on image, such as poor ranging accuracy, low reliability and complex system, a new visual passive ranging method based on re-entrant coaxial optical path is presented. The target image is obtained using double cameras with coaxial optical path. Since there is imaging optical path difference between the cameras, the images are different. In comparison of the image differences, the target range could be reversed. The principle of the ranging method and the ranging model are described. The relationship among parameters in the ranging process is analyzed quantitatively. Meanwhile,the system composition and technical realization scheme are also presented. Also, the principle of the method is verified by the equivalent experiment. The experimental results show that the design scheme is correct and feasible with good robustness. Generally, the ranging error is less than 10% with good convergence. The optical path is designed in a re-entrant mode to reduce the volume and weight of the system. Through the coaxial design,the visual passive range of the targets with any posture can be obtained in real time. The system can be widely used in electro-optical countermeasure and concealed photoelectric detection.     

Image contrast of impurity regions of semiconductor crystals in scanning electron microscopy

A critical survey of the current state of the problem of visualizing local impurity regions of semiconductor crystals in a scanning electron microscope (SEM) is presented. A new physicotechnical solution for monitoring impurity distributions in doped regions that allows us to increase the contrast between images of impurity sectors in a wide range of concentrations is proposed.     

The search for ultrashort bursts of cosmic ray intensity on the Andyrchi air shower array

A new data acquisition system that makes it possible to measure the count rate of each detector of the Andyrchi air shower array every millisecond is described. This new detection system allows us to search for ultrashort bursts of cosmic ray intensity when operating the array in the single-component detection mode. The method of data acquisition and analysis is discussed.     

掺杂半导体扫描电镜二次电子像

综述了用扫描电镜的二次电子像获得掺杂半导体衬度剖析的方法．实验发现掺杂半导体扫描电镜像对杂质浓度的灵敏度可以达到1016cm^-3，且空间分辨率高达nm量级，是最有可能发展成为下一代掺杂剖析成像的主流技术．文中还探讨了半导体掺杂衬度的可能的机理，详细介绍了两种主要机理：表面能带弯曲和样品外局域电场的出现．     

Electron optics for high throughput low energy electron microscopy

Novel electron-optical components and concepts aiming at improving the throughput and extending the applications of a low energy electron microscope (LEEM) have been developed. An immersion magnetic objective lens can substantially reduce e-e interactions and the associated blur, as electrons do not form a sharp crossover in the back-focal plane. The resulting limited field of view of the immersion objective lens in mirror mode can be eliminated by immersing the cathode of the electron gun in a magnetic field. A dual illumination beam approach is used to mitigate the charging effects when the LEEM is used to image insulating surfaces. The negative charging effect, created by a partially absorbed mirror beam, is compensated by the positive charging effect of the secondary beam with an electron yield exceeding 1. On substrates illuminated with a tilted beam near glancing incidence, large shadows are formed on even the smallest topographic features, easing their detection. On magnetic substrates, the magnetic flux leaking above the surface can be detected with tilted illumination and used to image domain walls with high contrast.